Integrated coaxial transducer

ABSTRACT

A coaxial transducer that uses lead zirconate titanate ceramic or other suitable material as an isolator between the conductors in a coaxial cable to transmit acoustic power at useful levels. The lead zirconate titanate ceramic is diced into thin disks and placed in between spacers made of much stronger insulating material. The coaxial cable is then integrated into a conventional double-armored steel tow cable with a typical diameter of 1″. This provides substantial longitudinal strength and provides crushing resistance to the lead zirconate titanate ceramic when the cable is being deployed or retrieved over a sheave under tension.

CROSS REFERENCES TO OTHER PATENT APPLICATIONS

This application is a divisional of prior U.S. patent application Ser.No. 12/287,154, now U.S. Pat. No. 7,985,924, filed on Sep. 29, 2008 andclaims the benefit under 35 U.S.C. §121 of the prior application'sfiling date.

This patent application is with the following related U.S. patentapplication Ser. No. 12/287,154 by the same inventor, Anthony A. Ruffa,and is co-filed with a related U.S. patent application entitled“Integrated Coaxial Transducer With Alternating Insulators”, by the sameinventor, Anthony A. Ruffa.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention is directed to tow cables for use with surfaceships and underwater vehicles. In particular, the present invention isdirected to integrating transduction material into the coaxial cablecomponent of a tow cable for use as an acoustic transducer, takingadvantage of the cable's long length to achieve significant acousticsource level.

(2) Description of the Prior Art

Surface ships and underwater vehicles often use tow cables while towingarrays of equipment such as hydrophones. Coaxial cables are commonlyintegrated into tow cables to transmit power and data to the tow body.Prior art tow cables and tow bodies adapted for use with ships andunderwater vehicles require a large handling system, a dedicated room,and a stern door. Mechanical problems plague the deployment andretrieval efforts. Furthermore, a heavy tow body leads to a steepcritical angle for the tow cable, requiring fairing and a specializedwinch with multiple drums. The winch (and foundation) rating must exceedthe cable breaking strength for safety. In light of some of theimplementation problems described above, several “soft tow” conceptshave been proposed, replacing an acoustic source in a tow body with adistributed acoustic source in a towed hose wound directly on a winch inan attempt to reduce handling complexity and increase vertical aperture.An acoustic source integrated into the tow cable will impact thehandling system minimally. Currently, there is a need for a new type ofacoustic transduction device, one integrated directly into a tow cableby replacing the insulating spacer in a coaxial cable with transductionmaterial for use in an armored tow cable, or a dipping sonar cable.

SUMMARY OF THE INVENTION

It is a general purpose and object of the present invention to implementan acoustic transduction device integrated directly into a coaxial cabletaking advantage of its long length to achieve significant acousticsource level.

It is a further purpose and object of the present invention tointegrating an acoustic source directly into a 1″ diameterdouble-armored steel tow cable instead of a much larger hose.

It is a further purpose and object of the present invention to transmitsignificant acoustic power with a tow cable.

The above objects are accomplished with the present invention throughthe use of lead zirconate titanate ceramic or other suitabletransduction material as the isolator between the conductors in acoaxial cable to transmit acoustic power at useful levels. The leadzirconate titanate ceramic is diced into thin disks, poled in the radialdirection, and placed in between spacers made of much strongerinsulating material. The coaxial cable is then integrated into aconventional double-armored steel tow cable with a typical diameter of1″. This design provides substantial longitudinal strength and providescrushing resistance to the lead zirconate titanate ceramic when thecable is being deployed or retrieved over a sheave under tension.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention and many of the attendantadvantages thereto will be more readily appreciated by referring to thefollowing detailed description when considered in conjunction with theaccompanying drawings, wherein like reference numerals refer to likeparts and wherein:

FIG. 1 a illustrates a side view of one embodiment of the coaxialtransducer with exposed components;

FIG. 1 b illustrates a cross sectional view of the one embodiment of thecoaxial transducer;

FIG. 2 a illustrates a side view of a second embodiment of the coaxialtransducer with exposed components;

FIG. 2 b illustrates a cross sectional view of the one embodiment of thecoaxial transducer; and

FIG. 3 illustrates a side view of a third embodiment of the coaxialtransducer with exposed components.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 a and 1 b, in the present invention, a coaxialcable 10 with a plastic jacket 12 is used as a continuous acoustic linesource with acoustic transduction material 14 replacing the insulationbetween the two conductors, the metal shield 16 and the center core wire18, in the coaxial cable 10. The combined coaxial cable and transductionmaterial are then integrated into a double-armored steel tow cable 20.The plastic jacket functions as a “water block”, keeping seawater fromthe coaxial cable. Making it thicker or of a more compressible materialcan further reduce stresses in the transduction sections. Finally, speedlimits can reduce cable tension, which also reduce stresses in thetransduction sections.

For example, a ¼″ diameter coaxial cable 10 filled with acoustictransduction material 14 in a mile long cable will have a volumeaccording to the following equation:

$\begin{matrix}{{\frac{\pi}{4}\left( \frac{1/4}{12} \right)^{2} \times 5280} = {1.80\mspace{14mu}{{ft}^{3}.}}} & (1)\end{matrix}$

Since the acoustic source level is usually proportional to the acoustictransduction material 14 volume/weight, a coaxial cable 10 with thisdesign has the potential to generate more acoustic power than sourcestypically used in traditional prior art tow bodies.

Referring to FIGS. 2 a and 2 b, in an alternative embodiment of thepresent invention, four ⅛″ coaxial cables 22, 24, 26, and 28 around acenter stainless steel tube 30 containing optical fibers 32 integratedinto a double-armored steel tow cable 20 provide the same volume ofacoustic transduction material as a single ¼″ coaxial cable 10, andprovide a more rugged design. Although in theory, four ⅛″ transducersmight allow transmission of a dipole or quadripole pattern, in practicethat does not occur for the following reasons: (1) the coaxial cables22, 24, 26 and 28 are often helixed inside the tow cable 20; and (2)even if they are not, the tow cable 20 itself twists since it is notperfectly torque balanced. Transmitting through a double-armored steeltow cable 20 will not lead to significant attenuation when the acousticwavelengths are much longer than the cable diameter.

Referring to FIG. 3, in a further embodiment of the present invention,the acoustic transduction material 14 is composed of a lead zirconatetitanate ceramic 34, which leads to a heavier tow cable 20 and increaseddepth. The lead zirconate titanate ceramic material 34 is diced intothin disks and placed in between spacers 36 made of much strongerinsulating material. The lead zirconate titanate density of 7500 kg/m³leads to 839 lb of total weight. The winch and sheave radii requirementsare usually thirty times the cable radius to extend cable life. Thisminimizes damage to the lead zirconate titanate material. To furtherreduce stresses on the transducer sections, the winch diameter can beincreased, e.g., to 40 times the cable diameter.

A lead zirconate titanate filled coaxial cable is not as fragile asother components integrated into tow cables (e.g., stainless steel tubesfilled with gel and optical fibers) and should be capable of survivingunder typical conditions as long as the minimum cable bend radius is notviolated.

Construction of the transducers for the coaxial cable involves thefollowing steps: A series of ¼″ or ⅛″ cylinders of transduction materialare made with holes for the center conductor. These cylinders are thenmanufactured into a single coaxial cable, poled in the radial direction,and integrated into the tow cable. To reduce bending stresses (and forease of manufacture) the transduction material is segmented beforeintegrating it into a coaxial cable. Non-conducting spacers in betweenthe transduction material sections provide design flexibility toincrease fracture toughness.

In operation, the long aperture (up to 1 mile) of the coaxial transducersteered to the broadside direction leads to very narrow transmit beams.The coaxial transducer cable is towed, or it is deployed from astationary ship, helicopter, or underwater vehicle. In the latter case,it would provide significant source level and a very narrow verticalbeam, which would be virtually impossible to generate from any otherdeployable system. A mile long tow cable acts as a giant side scansonar, illuminating both sides of a vehicle with as small as 0.02 degreebeams, depending on what the ocean environment can support.

The advantages of the present invention are as follows: The presentinvention provides a high source level. A mile long cable leads to atransduction volume of 1.80 ft³ within a ¼″ coax. Even a much shortercable should still lead to high volumes. The present invention hasnarrow broadside beam. This is especially significant for a “dipping”source deployed from a stationary underwater vehicle. The vertical cablewill generate a very narrow vertical broadside beam (less than 1 degree,depending on frequency). The present invention offers ease of handling.Since the transduction material is integrated into a 1″ diameter cable,it can be deployed from a small winch. The present invention does notcause cavitation. The sound pressure level per foot is low-far below thethreshold for cavitation.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives of the present invention, it isappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Additionally, feature(s) and/orelement(s) from any embodiment may be used singly or in combination withother embodiment(s). Therefore, it will be understood that the appendedclaims are intended to cover all such modifications and embodiments,which would come within the spirit and scope of the present invention.

1. A coaxial transducer for use in a tow cable comprising: a center coreconductor wire; a cylindrical jacket of acoustic transducer materialsurrounding said center core conductor wire; a cylindrical metal shieldconductor surrounding said cylindrical jacket of acoustic transducermaterial; a cylindrical jacket of plastic surrounding said cylindricalmetal shield conductor wherein said cylindrical jacket of plastic servesas a water tight protective covering; and an armored steel tow cablesurrounding said cylindrical jacket of plastic.
 2. The coaxialtransducer of claim 1, wherein the acoustic transducer material is poledradially.
 3. The coaxial transducer of claim 1, wherein the armoredsteel cable has a diameter of one inch.
 4. The coaxial transducer ofclaim 1, wherein the cylindrical jacket of plastic also cushions theacoustic transducer material to increase fracture toughness.
 5. Thecoaxial transducer of claim 1, wherein the cylindrical jacket of plasticis joined with a compressible material to further cushion the acoustictransducer material to increase fracture toughness.
 6. The coaxialtransducer of claim 1, wherein the winch has a radius greater thanthirty times the radius of the armored steel tow cable to furtherrelieve stresses in the acoustic transducer material.
 7. The coaxialtransducer of claim 1, wherein the operation limits of said coaxialtransducer involve a limited speed range to reduce tension, which willreduce stresses in the acoustic transducer material further preventingthe risk of fracture.